Adaptive direct conversion receiver

ABSTRACT

A method and apparatus is disclosed for improving performance of a communication receiver. An exemplary method comprises calculating a rate of error associated with a received signal at a first time; comparing the rate of error at the first time to a first threshold rate of error; if the rate of error at the first time exceeds the first threshold rate of error, increasing current provided to a mixer in the receiver; calculating a rate of error associated with a received signal at a second time; comparing the rate of error at the second time to a second threshold rate of error; and if the rate of error at the second time is less than the second threshold rate of error, resetting the mixer current.

RELATED APPLICATIONS

This is a continuation of U.S. application Ser. No. 10/131,166, filedApr. 23, 2002, which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to communication receivers and inparticular to direct conversion receivers.

BACKGROUND

Electronic communication is a popular form of exchanging informationbetween locations. When transmitting voice or data information it isgenerally desirable to maximize the amount of information within aparticular frequency band and minimize the error rate. This is true ofboth wireless and non-wireless applications.

To most efficiently utilize available bandwidth, communication standardsoften specify maximum transmit power levels and minimum separationbetween channels. As a result, challenges exist during signaldemodulation and signal recovery. Certain demodulation and signalrecovery operations, while effective, consume power at a high rate.While power consumption is a relevant consideration in any typereceiver, battery operated communication receivers are particularlysensitive to power usage issues. One example of a battery operationcommunication receiver is a receiver in a wireless telephone, such asfor example a cellular telephone.

In addition to power usage constraints, the cost and performance of thereceiver is also a consideration. By way of example, superheterodynereceivers are a widely adopted configuration for wireless communicationreceivers. However, as compared to a direct conversion or near zero IF(hereinafter referred to as direct conversion) receiver, superheterodynereceivers are undesirably expensive. As a result, direct conversionreceivers offer performance at a lower cost per unit thansuperheterodyne receivers. A superheterodyne receiver mixes the RFsignal down to an intermediate frequency (IF) and eventually down tobaseband. In contrast to superheterodyne receivers, direct conversionreceivers demodulate the received signal from the carrier frequency tothe baseband without use or passage through an intermediate frequency(IF). By eliminating hardware required to process the signal through theintermediate frequency, the cost of the direct conversion receiver isreduced.

While direct conversion receivers of the prior art enjoy cost advantagesover superheterodyne receivers, their use has drawbacks. One suchdrawback is a susceptibility to signal interference from unwantedextraneous signals, or jammers. Because the direct conversion receiverdoes not demodulate and filter at an intermediate frequency unwantedsignals may follow a signal of interest to the baseband. These unwantedsignals may interfere with signal reception, decoding, and processingthereby disrupting a user's ability to use the communication device orchannel. In some instances a cellular telephone system may drop the calldue to the interference from the unwanted signal. These interferingsignals need not be on adjacent or alternate channels to causeinterference to the demodulated desired signal. This is because onesource of unwanted signal disruption is generated within the receiver'sdemodulator by means of second order distortion products in the downmixer (or demodulator) itself. Therefore any two or more signals in theband as a whole but spaced apart by a frequency equal to or less thanthe desired signal bandwidth may generate a second order interferingsignal at baseband. Thus the ability to minimize second order productsin the receive chain is of vital importance.

An additional drawback of the prior art was an inability to determinethe cause of the poor reception. The poor reception may arise from aweak signal or an unwanted interfering signal being generated by secondorder products within the receiver.

Therefore, there is a need in the art for a communication receiver thatadopts the benefits of a direct conversion receiver (i.e., lower cost,fewer components, and lower power consumption) yet reduces theundesirable effects of the unwanted signals that may demodulate into thebaseband. There is also a need for a method and apparatus to aid indetermining the reason for the poor reception.

SUMMARY

The methods and apparatus described below provide a solution fordrawbacks that exist in the field of wireless communication receivers.In an example system comprising a direct conversion receiver aninterference signal may be received with the desired signal In the pastthis type of problem caused the error rate, such as the bit error rate(BER), to undesirably increase. Some proposed solutions, in attempt toimprove receiver linearity and thus reduce internally generatedinterference, force the receiver to permanently operate in a state ofhigh power consumption. While this may increase performance, theincreased power consumption resulting from permanent operation in astate of high power consumption undesirably reduces battery life.Reduced battery life results in reduced talk time and reduced standbytime.

To overcome the problems associated with the prior art and to provideadditional advantages in signal reception the method and apparatusdescribed herein is able to identify the reason or cause of the higherror rate. After determining the cause of the high error rate, themethod and apparatus described herein may selectively process the signalto reduce the error rate. It is contemplated that selective processingwill occur during periods when such selective processing will reduce theerror rate.

Various steps may be taken to reduce the error rate. In one embodimentthe current supplied to the mixer is increased to thereby reduce secondorder blocking products. Further, when the mixer is operating in a highcurrent consumption state the receiver may periodically or continuouslymonitors the error rate. If the error rate has decreased sufficiently,such as below a threshold, the demodulator operation returns to normalcurrent consumption levels. This provides the benefit of only operatingthe demodulator in a high current state during periods when high currentoperation is necessary to reduce the error rate. If, as a result of themonitoring, the error rate has not decreased below a threshold, then thedemodulator continues high current operation. In this manner the systemmonitors the error rate and high current demodulator operation onlyoccurs when the error rate is undesirably high and when the cause of thehigh error rate is such that the error rate would be reduced by thesteps described herein.

In one embodiment the error rate may be further monitored to determineif additional steps should be taken to reduce the error rate. Thisprovides the advantage of further reducing the error rate and henceimproving reception and reducing the likelihood of a call being dropped.In one embodiment the receiver is further configured to reduce the errorrate by monitoring and adjusting the phase offset, balance or both ofone or more aspects of the receiver.

During processing it is often beneficial to split the received signalinto separate components. For example some receivers separate a receivedsignal into I and Q components, which are 90 degrees out of phase. Usingone aspect of the invention the phase offset of the two or more signalcomponents are monitored and adjusted to bring the signal components tothe exact desired phase offset. In one embodiment a phase splitter,mixer, and/or automatic gain control unit are monitored and adjusted toinsure proper phase offset. In another embodiment the inherent balanceof each mixer, which forms part of the demodulator, is adjusted toprovide cancellation of the second order products. Through the use ofproper phase offset and amplitude matching the full canceling effects ofa split phase system may be realized. This adaptive balancing functioneffectively increases the receivers second order intercept point andthus reduces the internal generation of second order distortion productswhich might otherwise interfere with the desired signals' demodulationwithin the DSP.

The method and apparatus described herein provides numerous advantagesover systems of the prior art. In one embodiment these advantages arerealized with a direct conversion receiver. Direct conversion receiversprovide a lower cost alternative to superheterodyne receivers. Incontrast to systems of the prior art, one embodiment of the invention isable to determine when the receiver is experiencing a high error rate.In one embodiment action is taken to reduce the high error rate onlyduring periods of a high error rate. By selectively taking action toreduce the error rate only when the error rate is undesirably high,instances of high power consumption may be reduced.

Yet another advantage of the invention is its ability to determine thecause of a high error rate. By determining the cause of the high errorrate changes in receiver operation can selectively occur so that changesin receiver operation only occur when the change in receiver operationwill reduce the error rate. It is contemplated that in some instancesthe high error rate can not be reduced. In such an instance, there is noneed to increase power consumption of the receiver, such as increasingthe current supplied to the mixer, since such increased powerconsumption would not reduce the error rate. Thus, in one embodiment thereceiver operates in an error reducing high power consumption state onlywhen such operation will reduce the error rate.

Yet another advantage of the method and apparatus described herein isthat as a result of monitoring the error rate during periods in a highcurrent consumption such periods may be limited to periods 1) when thereceiver is producing a high error rate and/or 2) when operation in ahigh current consumption state will reduce the error. Thus, in oneembodiment the receiver, during periods of increased power consumptionto counter a high error rate, periodically monitors the error rate. Ifthe error rate is reduced below a desired level, then the receiver willresume operation at normal or low power consumption levels. As a resultof the invention, standby and talk time of wireless telephones areextended beyond those of the prior art while concurrently gaining thebenefits of a direct conversion receiver and reduced error rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a block diagram of an example embodiment of theinvention.

FIG. 2 illustrates an exemplary plot of exemplary communication signalswithin a radio frequency amplifier's frequency pass band.

FIG. 3 illustrates a block diagram of an example configuration of oneembodiment of the invention.

FIG. 4 illustrates an exemplary plot of an example communication signalin the baseband and the RF band with associated unwanted signalcomponents.

FIG. 5A illustrates an exemplary plot of an exemplary communicationsignal with unwanted signal components after a first method of receiveramplification adjustment.

FIG. 5B illustrates an exemplary plot of an exemplary communicationsignal with unwanted signal components after a second method of receiveramplification adjustment.

FIG. 6 illustrates an operational flow diagram of an example method oferror analysis.

FIG. 7 illustrates an operational flow diagram of an example method ofselective error reduction.

FIGS. 8A and 8B illustrates an operational flow diagram of analternative method of selective error reduction.

DETAILED DESCRIPTION

In the following description, numerous specific details are set forth inorder to provide a more thorough description of the present invention.It will be apparent, however, to one skilled in the art, that thepresent invention may be practiced without these specific details. Inother instances, well-known features have not been described in detailso as not to obscure the invention. In addition, the various aspects orembodiments described herein may be implemented alone or in anycombination.

FIG. 1 illustrates a block diagram of an example embodiment of theinvention. In this example embodiment a receiver 100 is configured foruse in a wireless communication device. The receiver 100 comprises anantenna 102 connected to a high frequency amplifier 104. In theembodiment of FIG. 1 the high frequency amplifier 104 is a radiofrequency amplifier. The output of the RF amplifier 104 feeds into ademodulator 108 and the output of the demodulator is provided to a gaincontrol unit 112. The gain control unit couples to a sampler 116. Theoutput of the sampler 116, which is provided on an output 128, issubject to further processing in apparatus subsequent to the receiver100.

In operation the antenna receives a signal traveling through the air,converts the signal energy to an electrical energy form and directs thesignal to the RF amplifier 104. The RF amplifier 104 may include afiltering system to insure only a band or range of desired frequenciesare amplified. The RF amplifier 104 increases the signal magnitude to alevel suitable for processing by the receiver 100. As is understood,signal processing at high frequency is generally undesirable.Accordingly, the demodulator 108 converts the high frequency carriersignal a signal at baseband. In one embodiment the receiver 100comprises a direct conversion receiver. In a direct conversion receiver,the single demodulator 108 converts the signal to baseband.

The demodulated signal is provided to the gain control 112. In oneembodiment the gain control comprises an automatic gain control (AGC)unit designed to adjust the baseband signal level to a level appropriatefor the sampler 116. The sampler 116 is configured to sample the analogsignal to thereby generate a digital version of the received signal. Oneexample of the sampler 116 is a 12 bit analog to digital converter,however, there are many other implementations of an analog to digitalconverter. Digital signals may be desirable for use in communicationsystems to provide advantages not available in analog systems.

It is contemplated that in some instances the antenna 102 may receiveand provide signals to the RF amplifier that contain unwanted orspurious signal portions located within the amplification band of the RFamplifier 104. FIG. 2 illustrates an example plot 200 of components of areceived signal located within a filter or RF amplifier's frequency passband. Voltage magnitude is represented on a vertical axis 204 whilefrequency is represented on a horizontal axis 208. The amplifier orfilter pass band 212 allows a signal of interest 216 to pass or beamplified. However, as can be seen the amplifier or filter also passesunwanted signal portions 220. These signal portions pass to subsequentstages of the receiver and may interfere with intended receiveroperation and signal recovery. Hence, it is desired to eliminate orreduce the effects of the unwanted signals 220.

To detect the presence of or overcome the undesirable effects of theunwanted signals 220 the embodiment of FIG. 1 includes error monitoringand receiver control systems. Returning to FIG. 1, the output of thesampler 116 is provided to an error detector 120. The error detector 120provides a signal to a controller 124 and in this exemplary embodimentthe controller may provide control signals to any one or more of the RFamplifier 104, the demodulator 108, and the gain control 112. Additionalcomponents may be interspersed among the shown apparatus to facilitateoperation of the receiver as would be understood by one of ordinaryskill in the art.

To achieve the advantages of the monitoring and receiver control systems120, 124 the error detector 120 is configured to monitor and process theoutput signal to determine an error rate. In one embodiment the errordetector 120 monitors a bit error rate (BER). If the error rate exceedsa predetermined level, it notifies the controller to provide controlsignals to the RF amplifier 104, demodulator 108, and/or gain control112. Through control of one or more of these apparatus and furthermonitoring of the sampler output by the error detector 120 thecontroller 124 can determine if the cause of the high error rate is fromthe unwanted signal portions 220. In some instances unwanted signalportions 220 may be responsible for a high error rate while in otherinstances other factors, such as a weak signal, may be responsible. Ifthe higher error rate is a result of an unwanted signal, such asinterference or a jammer, then steps may be taken to reduce the errorrate.

In one embodiment, upon detection of a high error rate the controllerreduces the amplification level of the RF amplifier 104 by a minimalamount, for example, 1 db, while optionally increasing the gain of thegain controlled 112 by a minimal level, such as for example the sameminimal level. This has the effect of reducing the second orderdistortion products generated by the jammers 220 in the demodulator 108by 2 dB while leaving the wanted signal at worst degraded by 1 dB. Thusthe signal jammer ratio has been improved by at least 1 dB. It, as aresult of this manipulation, the error rate decreases then the higherror rate can be assumed to be a result of the unwanted signal portionsgenerating second order distortion in the down converters associatedwith demodulator 108. Action can then be taken to reduce the high errorrate. In contrast, if the error rate is unchanged then the high errorrate can be assumed to not be a result of the unwanted signal portions.In this manner a determination is made as to the source or cause of thehigh error rate. Action can be taken to reduce the error rate based onthis analysis.

By way of example if the high error rate is a result of the unwantedsignal portions then the method and apparatus described below may beimplemented. If instead the source of the high error rate is not theunwanted signal portions then other remedial action may be taken. Theseactions include, but are not limited to, increasing transmit power bythe Base Station transmitter or other transmitter, transferring the callto a different cell site, adjusting phase offset, increasing RFamplifier amplification level, extending the phone's antenna, or movingto a different location.

One exemplary remedial action that may be taken if the high error rateis a result of the unwanted signal portions is to provide controlsignals to the demodulator 108 to process the signal in a manner thatmore thoroughly removes or reduces the second order distortion productsgenerated in one or more of the mixers by the unwanted signal portions.In one embodiment this comprises increasing a current level provided toone or more mixers in the demodulator 108. While such increased currentdesirably reduces the unwanted signal portions it undesirably increasespower consumption.

To overcome the drawback of increased power consumption the controller124 and error detector 120 may continually or periodically monitor theerror rate. Upon a decrease in the error rate the current supplied tothe demodulator may be reduced to thereby reduce the amount of time themixers operate in a high current state. In one embodiment a comparisonto a first threshold value controls when error reducing steps areinitiated and comparison to a second threshold value controls when errorreducing steps are de-activated. A second threshold, which is differentfrom first threshold, may be used during the comparison to prevent thesystem from hunting or oscillating between high and normal currentstates. In one embodiment the controller may briefly stop supplyingincreased levels of current to the demodulator to obtain accurate errorlevel information that is not otherwise effected by the increasedcurrent level supplied to a mixer. It is contemplated that additionalerror reducing steps may be taken by the receiver 100 upon detection ofa high rate of error. While these steps may increase power consumption,continual or periodic monitoring occurs to minimize the powerconsumption. Upon detection of the error rate falling below a first or asecond threshold the steps may be deactivated thereby restoring powerusage to normal levels.

FIG. 3 illustrates an example implementation of the embodiment shown inFIG. 1. In this example embodiment the receiver 300 comprises a directconversion receiver. As shown, an antenna 304 connects to a filter 308.The antenna 304 and filter 308 receive and isolate a desired signal. Inone embodiment the filter 308 is configured as a band pass filterconfigured to pass a select frequency band to subsequent stages of thereceiver. The output of the filter 308 provides the signal to a lownoise amplifier (LNA) 312. The LNA 312 increases the power level of thesignal to bring the low power signal received by the antenna 304 to alevel appropriate for processing by the receiver 300. The output of theLNA 312 connects to a second bandpass filter 316. The bandpass filter316 removes any DC bias or high frequency noise that is outside of thefrequency band of interest. It is contemplated that any type filter 308or 316 may be utilized.

A signal splitter 320 connects to and receives the output of the secondbandpass filter 316. Any type signal splitter 320 may be adopted foruse. The signal splitter 320 produces, from a single signal or waveinput, two or more output signals that offer acceptable phase andamplitude matching. In the embodiment shown in FIG. 3 the signalsplitter 320 is configured to separate the signal into two separatepaths, shown on lines 390, which are phase shifted apart by 180 degreesand amplitude matched,

In one embodiment the components 308, 312, 316, and 320 are collectivelycombined into a single device such as a low noise amplifier withamplitude and phase splitting capability, the phase splitting functionbeing provided by a differential output from filter 316. Thiscombination is shown inside dashed line 324. It should be noted thatalthough one particular embodiment is shown in FIG. 3, the scope of theinvention is not limited to this embodiment. One of ordinary skill inthe art may envision other combinations or embodiments which are coveredby the claims that follow.

The dual output of the phase splitter 320 feeds into an upper receiverbranch and a lower receiver branch. As these branches are generallyidentical the two branches are described in unison. Differences, if any,are noted when present. Mixers 330A, 330B receive signals on lines 390from the splitter 320 as shown. The inputs to the mixers 330A, 330B andthe outputs from the mixers are balanced. The mixers 330A, 330B alsoreceive inputs from a frequency divider 354, which in turn receivesinput from a signal generator 358. The divider 354 and generator 358 arecollectively referred to as a local oscillator. In one embodiment thesignal generator 358 creates a signal that is generally identical to butat twice the frequency of the carrier signal or some other multiplethereof. Use of the divider 354 helps to insure that the signalsprovided to the mixers 330A, 330B are of the same magnitude and exactly90 degrees out of phase, yet phase related to those signals provided bythe signal generator 358. Further, the divide ratio need not beconstrained to integer values. Indeed there are other benefits to usingnon-integer divide ratios.

The balanced outputs from the mixers 330A, 330B feed into automatic gaincontrol (AGC) devices 334A, 334B via connections 392. The output of theAGC devices 334A, 334B connect to bandpass filters 338A, 338B. The AGCdevices 334A, 334B and filters 338A, 338B operate to provide signals ofappropriate amplitude and frequency content to analog to digitalconverters (ADC) 342A, 342B. As is understood, some analog to digitalconverters 342A, 342B must receive a signal within a limited voltagerange as specified for the analog to digital converter. Any type ofmatched AGC 334A, 334B and filter 338A, 338B may be utilized to providea signal within the desired amplitude to the ADC 342A, 342B. In oneembodiment sampling of the signal occurs at 2000 KHz with 10 bits ofresolution. In another embodiment the ADC 342A, 342B are configured toaccept signals having a wide voltage range and hence the AGC 334A, 334Band filter 338A, 338B may be eliminated.

The outputs of the ADC 342A, 342B connect to a digital signal processor(DSP) 350. In other embodiments the DSP 350 may be replaced by any typeprocessor, control logic, ASIC type processing system or othercomponents capable of analyzing or changing one or more signals, devicesettings, device parameters or other aspects of circuit operation, andgenerating control or other type signals in response to the analysis.The DSP 350 is configured to receive and process the digital output fromthe ADC 342A, 342B. Any type processing may be performed as desired forcommunication signal analysis or as may be contemplated by one ofordinary skill in the art. While discussion of the DSP 350 is limited toaspects which are relevant to the invention, in use the DSP may beassigned any processing task.

In one embodiment the DSP 350 also connects to or communicates with oneor more of the LNA 312, the mixers 330A, 330B, and the AGC 334A, 334B.In the embodiment of FIG. 3 the DSP 350 also connects to the splitter320, and local oscillator devices 354, 358. Via the connection to theLNA 312 and the AGC 334A, 334B the DSP 350 may independently monitorand/or adjust the level of gain for either or both device. Via theconnection to the mixers 330A, 330B the DSP 350 may monitor and controlthe amount of current provided to the mixers. Via the connection to thesplitter 320, local oscillator devices 354, 358, and the mixers 330A,330B the DSP 350 may monitor and/or adjust the level of phase offsetbetween the upper and lower paths of the receiver.

To overcome the drawbacks of the prior art and provide furtherinnovations, the DSP 350 is configured to monitor the error rate of thereceived signal. One measure of an error rate is the bit error rate,which for purposes of discussion is used in the following description torefer to error rate. A large BER is understood to be undesirable. Onedrawback of systems of the prior art is difficulty in determining why ahigh BER is occurring. Because different action to remedy the high BERmay be necessary depending upon the cause of the high BER, it isdesirable to determine the cause of the high BER. After the cause of thehigh error rate is determined, appropriate error reducing action may betaken. The method and apparatus described herein may be made todetermine the cause of the high BER by adjusting the gain of one or moreamplifiers and monitoring for a change in the BER. If, after suchadjustment, the BER changes then the reason for the high BER may bedetermined.

FIGS. 4, 5A and 5B, discussed in conjunction with FIG. 3, are helpful inproviding a more detailed description of this operation. FIG. 41illustrates an example plot of an exemplary communication signal withunwanted signal components before and after demodulation. A horizontalaxis 208 represents frequency while a vertical direction representssignal amplitude. The frequency passband 212 of the filter 308 is shownby the band between F_(LF) and F_(HF). The desired signal 216A,modulated at the carrier frequency, lies between F_(C1) and F_(C2).Unwanted signal interference 220A is located within the passband 212 ofthe filter at a frequency F_(ci).

After demodulation by the mixer 330A, 330B, the desired signal 216Bresides at baseband between frequencies F₁ and F₂. However, the unwantedsignal components 220B are also present and reside at a frequency F_(i).As the interference signals 220B are second order products, mixeroperation may cause the interference signals 220B to become significantas compared to the desired signal 216B. Further, depending on theirrelative offsets to one another and the desired signal, they may betranslated to a frequency which falls between F1 and F2, i.e., directlywithin the baseband signal.

In one embodiment of the invention, the DSP 350 controls the LNA 312 toslightly increase its gain level. In one embodiment the level ofincrease is 1 dB. Concurrently, the DSP 350 may optionally reduce thelevel of gain in the AGC 334A, 334B to accommodate ADC 342A, 342B. Inone embodiment the level of reduction by the AGC 334A, 334B is inverselyproportional to the gain increase in the LNA 312. In one embodiment thelevel of reduction is 1 dB. In one embodiment the AGC 334A, 334B willautomatically decrease its level of gain to account for the change inLNA 312 gain. In one embodiment only the gain of LNA 312 is adjusted.

FIG. 5A illustrates an exemplary plot of an exemplary communicationsignal with unwanted signal components after adjustment of receiveramplifier settings. As can be seen by comparison of FIG. 5A to FIG. 4,in response to the increase in LNA gain the interference signals 504 hasincreased in magnitude relative to the desired signal 216B. This occursbecause increasing the gain of the LNA 312 causes a greater signal levelto be passed to the demodulator where the second order interferencesignals are generated within the mixer. Second order signals willincrease by the square of the gain increase in the RF stage, whereas thedesired signal 216B will only increase proportionally to the gainincrease. As a result of the increased presence or magnitude of theinterference signal 504, the BER will increase. In contrast, if the highBER is caused by an aspect other than the interference signal 504 thenthe change in gain level will not yield a change in the BER. In thismanner the reason or cause of the high error rates may be determined.Depending on the spacing between the jammers 220A, it is possible thatthey could be translated to a range of frequencies which lie directlybetween F1 and F2 resulti in severe disruption to the desired signal.

In an alternative embodiment the above described analysis is achieved bydecreasing the gain of the LNA 312 and increasing the gain in the AGC334A, 334B. Because a lower level of gain is occurring in the RF stagethe signals passed to the demodulator where the second orderinterference signals 504 are generated will decrease by the square ofthe gain decrease in the RF stage, whereas the desired signal 216B willonly decrease proportionally to the gain increase. As a result of thedecreased presence or magnitude of the interference signal 504, the BERwill decrease. FIG. 5B illustrates an exemplary plot of an exemplarycommunication signal with unwanted signal components after alternativeadjustment of receiver amplifier settings. As shown the interferencesignal 508 is reduced as compared to the desired signal 2168. Thus, thereduction the interference signal 508 and thus the BER, indicates thecause of the high BER is from interference signals. In contrast, if thehigh BER is caused by an aspect other than the interference signal 220Bthen the change in gain level will not yield a change in the BER. Inthis manner the contributing factor or reason for the high error ratemay be determined.

It is contemplated that in various embodiments only the LNA gain may beadjusted or only the AGC gain may be adjusted. It is furthercontemplated that both the LNA gain and the AGC may be adjusted eitherby increasing the LNA gain while decreasing the AGC gain or bydecreasing the LNA gain while increasing the AGC gain.

In another embodiment the above-described method and apparatus fordetermining the cause of the high error rate is combined with a methodand apparatus to selectively improve receiver operation to therebyreduce affects of the interference signal. In reference to FIG. 31 upondetection that the BER has exceeded a predetermined level, such as afirst threshold, the DSP 350 may send a signal, such as a control signalor current signal, to the mixers 330A, 330B. Increasing the currentsupplied to the mixers 330A, 330B improves mixer operation during anoverload situation such as when receiving an interference signal 220.With the increased current the mixer input intercept point for secondorder products is improved and the error rate will decrease. During aperiod of increased current operation the error rate can be periodicallyor intermittently monitored such as by comparison to a second threshold.If the monitoring reveals that the interference signals are no longergenerating an acceptably high error rate then the current provided tomixer 330A, 330B may be reduced to prior levels to reduce powerconsumption. Hence, in one embodiment the receiver is configured to onlyoperate the mixer in a high current state during periods when the errorrate is high and only when the high error rate is caused by second orderblocking signals, such as caused by interference signals. In oneembodiment the BER is monitored to determine when to reduce the currentlevel used for mixer operation. FIG. 7, described below, discusses thisoperation in more detail.

In another embodiment a method and apparatus is provided to reduce theerror rate and improve receiver operation. In reference to FIG. 3, theDSP 350 monitors for and detects a high error rate. Upon detection of anundesirably high error rate the DSP 350 may monitor and adjust theoperation of one or more of the splitter 320, the mixer 330A, 330B andthe AGC 334A, 334B to insure that the internal balanced signal output ofeach mixer has the appropriate phase difference (typically 180 degrees)and that the phase offset between the upper path and lower path (I and Qcomponents) is 90 degrees. If the phase difference at each individualmixer output is other than 180 degrees, the second order products maynot be entirely canceled and instead passed to amplifiers 330A and 330B.FIG. 8A and 8B describes this operation, in conjunction with the methodof FIG. 7 in more detail.

FIG. 6 illustrates an operational flow diagram of an example method ofdetermining a cause of errors in a received signal. This is but oneexemplary method of determining the cause of error in a received signal.It is contemplated that other methods of operation may be enabled by oneof ordinary skill in the art without departing from the scope of theclaims. At a step 600 the receiver obtains a signal. Any type of signalmay be received or obtained and the system may comprise any type ofwireless or non-wireless system. In one embodiment the system comprisesa receiver in a cellular telephone. In one embodiment the receivercomprises a direct conversion receiver operating under the principles ofcode division multiple access (CDMA) technology. After receiving thesignal the receiver at step 604, processes the signal according to thestandard operation of the receiver. Any type processing may occur.

At a step 608 the receiver monitors the error rate. In one embodimentthe bit error rate (BER) is monitored by a digital signal processor(DSP). Thereafter, at decision step 612 a comparison occurs between themonitored BER and a threshold value. In one embodiment a DSP performsthe comparison. The threshold value may comprise a predetermined valueabove which error decreasing actions may be taken to reduce the errorrate. The threshold value may comprise a predetermined value at which adetermination is made regarding the cause of the high error rate. If theerror rate is not above the threshold then the operation returns to step600.

Alternatively, if at decision step 612 the operation determines that theerror rate is above the threshold then the operation advances to a step616. At step 616 the receiver, reduces the gain to the RF amplifier andincreases the gain of the baseband amplifier. In one embodiment thiscomprises reducing the gain of a low noise amplifier and increasing thegain of an AGC unit. In an alternative embodiment only the gain of theLNA is adjusted.

At a step 620 the receiver monitors the error rate. Based on themonitoring of step 620 at a decision step 624 a determination is madewhether the error rate decreased. If at decision step 624 the rate hasnot gone down, then at step 628 a determination can be made that thecause of the error rate is not a result of unwanted signal components,an interference signal and/or second order blocking signals.Alternatively, if at decision step 624 it is determined that the errorrate decreased then at step 632 a determination can be made that thehigh error rate is a result of an interference signal and/or secondorder blocking signals. Thus the method provides means to determine oneor more causes of a high error rate.

FIG. 7 illustrates an operational flow diagram of an example method ofselectively improving receiver performance. This is but one exemplarymethod of reducing the error rate associated with a received signal. Itis contemplated that other methods of operation may be enabled by one ofordinary skill in the art without departing from the scope of theclaims. At a step 700 the receiver receives a signal and at a step 704the receiver processes the signal. In one embodiment the processingyields an error rate, such as a bit error rate. At a step 708 theoperation monitors the error rate. Based on the monitoring adetermination is made whether the error rate is above the threshold orbelow the threshold. This occurs at a decision step 712.

If at decision step 712 the error rate is not above the threshold thenthe operation returns to step 700 and the receiver continues receivingand monitoring the received signal. Alternatively, if at decision step712 the error rate is above the threshold then the operation advances toa step 716. At step 716 the receiver reduces the gain of the RFamplifier and increases the gain of the baseband amplifier. In oneembodiment any permutation of RF amplifier gain adjustment and basebandamplifier gain adjustment may occur. The baseband amplifier gain may ormay not be adjusted. The receiver again monitors the error rate at step720. At a decision step 724 a determination is made regarding if theerror rate changed after the changes made at step 716. If the error ratedid not change then the determination can be made, at a step 728, thatthe high error rate is not a result of unwanted signal components. Theoperation then returns to step 700.

In contrast, if at decision step 724 the system determines that theerror rates decreased then the operation progresses to a step 732. Atstep 732 any action or modification to receiver operation may occur toreduce the error rate. As can be understood it is desirable to firstdetermine the cause of the high error rate and thereafter take actiontailored to reduce the error rate. In the example method of operationshown in FIG. 7, at step 732 the amount of current supplied to the mixeris increased and receiver operation is continued. Increasing the amountof current supplied to the mixer will reduce second order products andthereby reduce the error rate. This is but one possible action that canbe taken to reduce error.

It is generally understood that continued operation when the mixer isconsuming high levels of current will reduce talk time and standby time.Accordingly at decision step 736 the system monitors if the error rateis sufficiently decreased so that the mixer current consumption may berestored to normal levels. Thus, if at decision step 736 the error rateis sufficiently reduced then the operation progresses to a step 744wherein the mixer current is reset to normal levels. In one embodimentstep 736 comprises comparison of the error rate to a second threshold.Thereafter the operation returns to step 700 for continued receiveroperation. Alternatively, if at decision step 736 the error rate has notsufficiently been reduced, such as due to changing channel orinterference conditions, then the operation progresses to a step 740. Atstep 740 the operation of the receiver continues with the current supplyto the mixer maintained at a higher level. After step 740 the operationreturns to step 736 and the monitoring continues. In this manner themixer only operates in a state of high current consumption duringperiods when the error is undesirably high. Moreover the mixer onlyoperates in a high current state when the high error rate can beremedied by operating the mixer in an increased current consumptionstate.

FIG. 8 illustrates an operational flow diagram of an alternative examplemethod of selectively improving receiver performance. Since portions ofFIG. 8 are generally similar to FIG. 7 only the differences in FIG. 8are discussed below. Starting at a step 724, a determination is madewhether the error rate is decreased as a result of the manipulation ofstep 716. Thereafter, the operation advances to step 724 or 728. At step728 no action occurs while at step 800 the mixer current is increased toreduce the error rate. Thereafter, in the embodiment of FIG. 8B, theoperation advances to a decision step 804. At decision step 804 anotherdetermination is made whether the error rate is below a threshold suchas the second threshold. If the error rate is now sufficiently below thesecond threshold, the operation advances to step 808. At step 808 themixer current is restored to normal levels and the operation returns tostep 700.

Alternatively, if at step 804 the error rate is not sufficiently below athreshold value such as for example a second threshold value, then theoperation advances to a step 812. At step 812 the receiver analyzes thephase alignment of the signal traveling through the upper and lowerpaths of the receiver. In one embodiment the signal is preferably 90degrees out of phase. If the signals are not phase offset by the desiredoffset then error may occur. At a decision step 816 a determination ismade whether the phase is mis-aligned. The DSP is able to compare therelative phases of the I and Q channels and adjust the phase andamplitude response as required. If it is determined that the phase ismis-aligned then the operation advances to step 824 and the receivercontrols one or more components of the splitter or mixer to adjust thephase to the desired level of offset, also the amplitude if there isimbalance. Further there maybe phase imbalance within the phase splitter320 itself. This imbalance will likely impair the IIP 2 of thedemodulators 330A and 330B. To minimize this issue the DSP 350 may optto incrementally shift the phase offsets of splitter 320 such that a 180degree balance is maintained for signals 390. The direction of requiredincremental can be determined by measuring the difference between I andQ channels. Thereafter, the operation returns to step 812 and theoperation is repeated until the proper phase offset is achieved. If atstep 816 the phase is properly aligned then the operation advances to astep 820. At step 820 the operation returns to step 804. The monitoringcontinues in this manner.

It will be understood that the above described arrangements of apparatusand the method therefrom are merely illustrative of applications of theprinciples of this invention and many other embodiments andmodifications may be made without departing from the spirit and scope ofthe invention as defined in the claims.

1. A method for reducing a rate of error in an output of a receivercomprising: calculating a rate of error associated with a receivedsignal at a first time; comparing the rate of error at the first time toa first threshold rate of error; if the rate of error at the first timeexceeds the first threshold rate of error, increasing current providedto a mixer in the receiver; calculating a rate of error associated witha received signal at a second time; comparing the rate of error at thesecond time to a second threshold rate of error; and if the rate oferror at the second time is less than the second threshold rate oferror, resetting the mixer current.
 2. The method of claim 11 whereinthe second threshold rate for error is less than the first thresholdrate of error.
 3. The method of claim 1, further including adjustingphase offset between quadrature separated signals if the second rate oferror is greater than the second threshold rate of error.
 4. A methodfor reducing a rate of error in an output of a receiver comprising:calculating a rate of error associated with a received signal at a firsttime; comparing the rate of error at the first time to a first thresholdrate of error; if the rate of error at the first time exceeds the firstthreshold rate of error, adjusting amplification applied to the receivedsignal; calculating a rate of error associated with a received signal ata second time; comparing the rate of error at the second time to therate of error at the first time; and if the rate of error at the secondtime is less than the rate of error at the first time, increasingcurrent provided to a mixer in the receiver.
 5. The method of claim 4,further comprising: calculating a rate of error associated with areceived signal at a third time; comparing the rate of error at thesecond time to the rate of error at the third time; and if the rate oferror at the third time is less than the rate of error at the secondtime, resetting the mixer current.
 6. A system for reducing the biterror rate in a wireless receiver comprising: a high frequency amplifierconfigured to amplify a received signal; a mixer configured todemodulate the amplified signal to create a baseband signal; a samplingunit configured to convert an adjusted baseband signal into a digitalsignal; an error detection unit configured to process the digital signalto determine an error rate; and a controller configured to compare theerror rate to one or more threshold values and selectively increase andreset a current level provided to the mixer based on the comparison.